In recent years, densification of a communication device has been essential in various data centers, and an aspect that a plurality of optical fiber core wires are mounted to one of the plug main bodies has become accordingly used widely.
Further, in view of improvement of a connecting workability in an optical connector ferrule, there has been provided a so-called MPO connector (an optical connector structured such that a multi-core optical connector ferrule defined by JIS-C5982 standard is stored in an inner portion of a plastic housing), in recent years.
Conventionally, as shown in FIGS. 17A to 17D and FIGS. 18A to 18C, an adapter main body 20 is formed into an approximately rectangular parallelepiped polygonal tubular shape, elastic locking portions 22 are integrally provided in both front and rear ends of right and left inner walls thereof so as to protrude in a facing manner toward plug insertion and removal opening portions 21A and 21B which are communicated back and forth. Both optical fiber core wires are optically connected by insertion of plug main bodies respectively into the plug insertion and removal opening portions 21A and 21B, as shown in FIGS. 20A and 20B.
Further, a key groove 19 with which a key projection (not shown) in the plug main body 10 side mentioned later engages is formed along a sliding direction of the plug main body 10, at the center of an inner surface of a lower wall portion in one plug insertion and removal opening portion 21A of the adapter main body 20, and at the center of an inner surface of an upper wall portion in the other plug insertion and removal opening portion 21B.
Further, approximately at the centers of both the right and left side surfaces of the adapter main body 20, there are formed locking projections 21 for locking the adapter main body 20 to an opening edge portion of a mounting opening portion for a panel when mounting to the mounting opening portion for the panel (not shown).
In the meanwhile, an MPO type plug main body 10 stores a ferrule 12 attached to a front end of an optical fiber tape core wire (not shown), in a front end (a forward end) of a sleeve-shaped housing 11, as shown in FIGS. 19A to 19C. Further, a spring 15 elastically biasing the ferrule 12 to a forward side of the plug main body 10 is provided within the housing 11.
Further, it is provided with a tubular coupling 13 which is outward inserted into a recess 17 formed in the housing 11, is arranged so as to be slidable in a range of movement secured in relation to the housing 11 in an axial direction thereof, and is elastically biased to a forward side of the plug main body 10 by a spring 16, and a spring push 14 which is mounted to an opposite rear end portion to a front end where the ferrule 12 of the housing 11 is arranged, and locks and supports a rear end of the spring 15.
Further, small holes 18 for inserting a pin (not shown) are provided in bilaterally symmetrical positions in a front end side of the coupling 13, and the coupling 13 can be disassembled from the housing by simultaneously inserting both pins of a clamp-shaped pin tool (not shown) having a pair of pins into the respective small holes 18.
The insertion of the plug main body 10 into the adapter main body 20 is achieved by a worker's operation of pressing a portion which is positioned in a rear side of the coupling 13 in the plug main body 10, for example, the housing 11 or a boot B, as shown in FIGS. 19A to 19C.
In the meanwhile, the removal of the plug main body 10 from the adapter main body 20 is achieved by pulling in the coupling 13 rearward against an elastic biasing force of the spring 16.
More specifically, as shown in FIGS. 19A to 19C, a front end of the coupling 13 is pressed by an elastic locking portion 22 and is once moved backward by inserting a front end side of the housing 11 in the plug main body 10 into the plug insertion and removal opening portion 21A of the adapter main body 20. The housing 11 is provided with a pair of front and rear locking convex portions 31a and 31b in a protruding manner via a catch portion 31 arranged in a front end thereof, and the elastic locking portion 22 tightly eats into the catch portion 31 so as to be locked after a locking projection 22a formed in a front end inner surface thereof climbs over the front side locking convex portion 31a. 
Further, the coupling 13 slides and returns forward since the coupling 13 is always biased to a front side of the plug main body 10 by a spring 16, and an outer surface of the elastic locking portion 22 is coated and retained by the front end inner surface of the coupling 13 and disenables removal of the housing 11.
When removing the plug main body 10, the coupling 13 is slid rearward in a state in which the locking projection 22a of the elastic locking portion 22 is engaged with the catch portion 31 of the housing 11. At this time, the catch 31 in a state in which the locking projection 22a is engages is exposed. Consequently, the locking projection 22a engaged with the catch portion 31 of the housing 11 climbs over the locking convex portion 31a by pulling out the plug main body 10. Further, at the same time that the locking projection 22 is released from a gap between the housing 11 and the coupling 13, the coupling 13 slides and returns forward by the spring 16, and the front end of the coupling 13 covers the catch portion 31a. 
Further, as shown in patent literature 1, there has been known an optical connector adapter with shutter, including an adapter main body which is formed into an approximately rectangular parallelepiped shape, a plug insertion and removal hole which is formed in a penetrating manner in the adapter main body, a pair of latch members which are mounted to an inner surface of the plug insertion and removal hole so as to be spaced at an interval in a width direction of the adapter main body, a pair of latch member mounting grooves which are formed in an inner surface of the plug insertion and removal hole so as to be spaced at an interval in the width direction of the adapter main body, a penetration portion which is formed in a lower surface of the adapter main body in a thickness direction so as to be communicated with the plug insertion and removal hole, a window member which is mounted to the penetration portion, a shutter plate which is arranged in the plug insertion and removal hole, and a stopper fitting which is installed to an outer surface of the adapter main body.